1. Field of the Invention
This invention relates to a sub-atmospheric pressure gas delivery system for supplying gas to a gas-consuming process facility such as a semiconductor manufacturing tool, wherein the system utilizes sub-atmospheric gas supply vessels and is auto-switchable in character from an empty vessel to a full one without pressure spikes or flow perturbations.
2. Description of the Related Art
In the semiconductor manufacturing field, source vessels of gaseous chemical reagents are commonly used to supply process gases to various tools in the manufacturing facility. These source vessels have traditionally been high pressure gas cylinders mounted in gas cabinets of various designs. The gas cabinets provide a controlled microenvironment for the gas cylinders, and are typically equipped with flow circuitry, flow regulator devices (e.g., mass flow controllers, restricted flow orifice elements, flow control valves, valve actuators, etc.), and gas flow/process monitoring, control and output elements such as displays, gauges, recorders, sensors, microprocessors, central processing units (CPUs), and the like.
In order to provide for continuity of process operation, the gas cabinet may contain multiple gas cylinders manifolded together and arranged for sequential use, and coupled with mass flow controllers (MFCs) to regulate the flow of the dispensed gas. In such gas cabinet arrangement, a cylinder, once it is exhausted or nearing an empty condition, is xe2x80x9cswitched outxe2x80x9d of active feed relationship to the associated gas-consuming process, and replaced with a xe2x80x9cswitched inxe2x80x9d fresh cylinder containing the gaseous reagent to be supplied to the associated process. The switching may be manual in character, but more typically is an automated operation (xe2x80x9cauto-switchoverxe2x80x9d) under the control of a computer-based monitoring and control system.
Auto-switchover of high pressure gas cylinders is a common practice, for which gas cabinets are readily commercially available from most gas cabinet manufacturers. The auto-switchover operation itself is easily accomplished, because high pressure gases (e.g., at 1500 psig supply pressures) from supply cylinders are typically regulated down to a lower pressure level (on the order of 35 psig, for example) for use in the semiconductor manufacturing facility. The auto-switchover takes place at the lower, regulated pressure, making the change seamless in character. This change does not upset the MFCs in the flow circuitry joined to the high pressure cylinders.
High pressure gas cylinders, however, present a safety issue in respect of possible leakage of gas from the valve head or bulk dissemination of the gas in the event of rupture of the cylinder. The gases typically used in the semiconductor manufacturing facility and supplied from high pressure gas cylinders are highly toxic, and may also be pyrophoric and/or explosive in character.
As a result of these dangers, sub-atmosphericpressure gas supply systems, e.g., of the type disclosed in U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, have come into widespread usage in the semiconductor manufacturing facility. The sub-atmosphericpressure gas supply system described in the Tom et al. patent utilizes a storage and dispensing vessel, which may be of the same type as used for high pressure gas storage, but which contains a physical adsorbent material holding a sorbate gas (e.g., a hydride gas, halide gas, gaseous organometallic Group V compound, or the like), in an adsorbed state, at sub-atmosphericpressure.
The sorbent medium employed in the gas supply system disclosed in the Tom et al. patent may comprise a zeolite or activated carbon material. The gas is dispensed in use of the system by pressure differential-mediated and/or thermal differential-mediated desorption, optionally with flow of a carrier gas through the gas storage and dispensing vessel providing a concentration differential effecting desorption of the gas from the physical adsorbent in the vessel.
As a result of their sub-atmosphericpressure operating characteristic, the physical adsorbent-based gas supply system of the Tom et al. patent have been widely adopted as a safe and reliable gas supply product for semiconductor manufacturing operations, in preference to high pressure cylinder gas sources.
Despite their benefits, however, when used in manifolded arrangements involving switching from a depleted gas supply vessel to a fresh (full) vessel in the operation of the system, as in gas cabinets containing two or more gas supply vessels arranged for such switchover operation, sub-atmospheric pressure gas sources cause substantial pressure perturbations to occur in the associated flow circuitry.
Such pressure perturbations destabilize the MFCs in the flow circuitry joined to the sub-atmospheric pressure gas sources.
As a result, the flow rate of gas supplied to the downstream process is likewise destabilized and may be higher, lower or significantly variable in relation to the desired set point flow rate for the downstream process.
These switchover-related variations from normal desired operating conditions can result in wafer defects in the semiconductor manufacturing operation, which in turn may necessitate costly reworking or even rejection of the corresponding semiconductor product articles.
It would therefore be a significant advance in the art to provide an improved means and method for operation of manifolded sub-atmospheric pressure gas supply vessels, which avoid pressure spikes and other adverse flow behavior incident to switchover of the sub-atmosphericpressure vessels, in a gas cabinet or otherwise.
It is accordingly an object of the present invention to provide an improved auto-switching sub-atmospheric pressure gas delivery system that overcomes such pressure perturbation problems.
It is another object of the invention to provide an auto-switching sub-atmospheric pressure gas delivery system for sub-atmospheric pressure sorbent-based gas storage and dispensing vessels in a gas cabinet containing such auto-switchable vessels.
It is a still further object of the invention to provide an auto-switching sub-atmospheric pressure gas delivery system that is easily fabricated and efficiently operable to minimize pressure perturbations in switchover operation of the system.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.
The present invention relates to an auto-switching sub-atmospheric pressure gas delivery system for dispensing of sub-atmospheric pressure gas for use in applications such as the manufacture of semiconductor products.
In one aspect, the invention relates to an auto-switchable sub-atmospheric pressure gas delivery system including a plurality of sub-atmospheric pressure gas supply vessels coupled to a valved gas dispensing manifold, wherein subsequent to auto-switching an on-line gas supply vessel is arranged to dispense gas for flow through the valved gas dispensing manifold for discharge therefrom, with flow control valve in the manifold being maintained in an open dispensing state during the flow through the valved gas dispensing manifold for discharge therefrom.
The system according to such aspect of the invention comprises means for restrictively flowing gas from the on-line gas supply vessel into the valved gas dispensing manifold to progressively build pressure in the valved gas dispensing manifold to a gas dispensing pressure level for said discharge with the flow control valve in the open dispensing state, and for opening the flow control valve to the open dispensing state after said gas dispensing pressure level has been reached.
In such auto-switchable sub-atmospheric pressure gas delivery system, the aforementioned means may for example be means of the following type:
(i) a bleed flow passage in the flow control valve;
(ii) a gas flow by-pass loop associated with the flow control valve;
(iii) a valve actuator programmably arranged to actuate the flow control valve in a pressure-building mode selected from the group consisting of:
(a) progressively opening of the flow control valve; and
(b) pulsed opening/closing of the flow control valve.
In another aspect, the present invention relates to auto-switching sub-atmospheric pressure gas delivery system, comprising:
a gas dispensing manifold;
a plurality of sub-atmospheric pressure gas supply vessels, each said gas supply vessel being joined to the gas dispensing manifold and including a vessel valve that is selectively openable to establish gas flow communication of the gas supply vessel with the gas dispensing manifold, and selectively closeable to terminate gas flow communication of the gas supply vessel with the gas dispensing manifold;
a plurality of flow control valves in the gas dispensing manifold, each associated with a corresponding one of the plurality of sub-atmospheric pressure gas supply vessels and positioned in the manifold downstream from vessel valve of the associated sub-atmospheric pressure gas supply vessel;
a plurality of bleed flow passages, each associated with a corresponding one of the flow control valves in the gas dispensing manifold and arranged to flow gas therethrough in bypassing relationship to the associated flow control valve, at a restricted low flow rate in relation to flow rate of gas through the associated flow control valve when the associated flow control valve is open and gas is flowed therethrough from an associated sub-atmospheric pressure gas supply vessel; and
a controller arranged to selectively operate the flow control valves so that a flow control valve is opened only after (i) gas flow is established by opening a vessel valve of the associated sub-atmospheric pressure gas supply vessel, and (ii) gas flow through the bleed flow passage associated with that flow control valve has caused gas pressure in the manifold to rise to an operating level for gas dispensing operation involving flow of gas out of the manifold.
Another aspect of the invention relates to an auto-switching sub-atmospheric pressure gas delivery system comprising a gas cabinet containing a gas delivery manifold arranged for delivering gas from the gas cabinet, and a plurality of gas supply vessels each coupled in latent gas flow communication with the manifold for said delivery of gas from the gas cabinet from a selected one of the plurality of gas supply vessels, with means for valvably establishing gas flow from the selected one of the plurality of gas supply vessels to the manifold and valvably isolating selected other(s) of the plurality of gas supply vessels from gas flow communication with the manifold, a controller for auto-switching of the vessels in sequence for flow of gas from a selected one of the plurality of gas supply vessels to the manifold until its depletion followed by switching of a new selected one of the plurality of gas supply vessels to the manifold and isolation of the selected other(s) of the plurality of gas supply vessels, and restricted flow means for flowing gas from a selected one of the gas supply vessels at auto-switching thereof into gas flow communication with the manifold to pressurize the manifold prior to valvably establishing gas flow from the selected one of the plurality of gas supply vessels to the manifold.
In a further aspect, the invention relates to a method of dispensing gas from an assembly of sub-atmospheric pressure gas supply vessels secured to a valved manifold arranged to selectively connect successive ones of the gas supply vessels in sequence to the manifold, by opening of an associated valve isolating a selected vessel from gas communication with the manifold and closing of an associated valve of a vessel depleted of gas, said method comprising restrictively flowing gas from the selected vessel into the manifold to pressurize the manifold to an operating pressure level during switchover of gas supply from said vessel depleted of gas, to a previously isolated selected vessel.
A still further aspect of the invention relates to a method of auto-switching sub-atmospheric pressure gas delivery, comprising:
providing a sub-atmospheric pressure gas delivery system described hereinabove;
flowing gas from a selected one of said plurality of sub-atmospheric pressure gas supply vessels to the gas dispensing manifold at a dispensing pressure, with the vessel valve of said selected one of said gas supply vessels open, the flow control valve associated with the selected one of the gas supply vessels open, and the vessel valve of a second one of said gas supply vessels closed, until pressure in the selected one of the gas supply vessels has declined to a level requiring switchover;
closing the vessel valve of said selected one of said gas supply vessels open and the flow control valve associated therewith, and concurrently opening the vessel valve of the second one of said gas supply vessels while maintaining the flow control valve associated with the second one of said gas supply vessels closed;
bleeding gas from the second one of said gas supply vessels through the bleed flow passage associated with the flow control valve for said second one of said gas supply vessels, until the gas pressure in the manifold rises to dispensing pressure; and
when gas pressure in the manifold has risen to dispensing pressure, opening the flow control valve for said second one of said gas supply vessels.
Another aspect of the invention relates to an auto-switching sub-atmospheric pressure gas delivery method comprising providing a gas cabinet containing a gas delivery manifold arranged for delivering gas from the gas cabinet, and a plurality of gas supply vessels each coupled in latent gas flow communication with the manifold for said delivery of gas from the gas cabinet from a selected one of the plurality of gas supply vessels, with means for valvably establishing gas flow from the selected one of the plurality of gas supply vessels to the manifold and valvably isolating selected other(s) of the plurality of gas supply vessels from gas flow communication with the manifold, and auto-switching the vessels in sequence for flow of gas from a selected one of the plurality of gas supply vessels to the manifold until its depletion followed by switching of a new selected one of the plurality of gas supply vessels to the manifold and isolation of the selected other(s) of the plurality of gas supply vessels, and flowing gas from a selected one of the gas supply vessels at auto-switching thereof into gas flow communication with the manifold to pressurize the manifold prior to establishing gas flow from the selected one of the plurality of gas supply vessels to the manifold.
Other aspects, features and embodiments in the invention will be more fully apparent from the ensuing disclosure and appended claims.